Turbine blade and method for producing a turbine blade

ABSTRACT

A method is for producing a turbine blade, in particular, a gas turbine blade, comprising a head, a foot, and a blade section, in addition to an internal canalization system, including individual channels through which coolant gas can pass along a flow path within the turbine blade. The turbine blade also includes a throttle device which influences the passage of the coolant gas without impairing the flow of the coolant gas in the intake area. The throttle device is located in the rear section of the flow path, and is positioned upstream of the exit openings.

This application is the national phase under 35 U.S.C. §371 of PCTInternational Application No. PCT/EP00/10678 which has an Internationalfiling date of Oct. 30, 2000, which designated the United States ofAmerica, the entire contents of which are hereby incorporated byreference.

FIELD OF THE INVENTION

The invention generally relates to a turbine blade, in particular a gasturbine blade. More preferably, it relates to one having a tip region, aroot region and a blade-body region. It may have an inner passage systemof individual passages, through which cooling gas can be directed on aflow path inside the turbine blade, and a throttle device influencingthe throughflow of the cooling gas. Cooling gas may be directed in thepassages from the root region through the blade-body region to the tipregion and can be diverted in the opposite direction. Also, it may haveoutlet openings for discharging the cooling gas from the turbine blade,with these outlet openings being arranged on the outflow side of theturbine blade. The invention may generally relate to a method ofproducing a turbine blade. In order to achieve a high efficiency duringthe operation of a turbine with an action fluid, in particular of a gasturbine operated with a gas, the action fluid is heated to a hightemperature. In a gas turbine with a combustion chamber for producingthe hot gas, the guide and moving blades nearest to the combustionchamber are subjected to a throughflow of cooling gas so that theywithstand the high temperatures prevailing there, which are partly abovethe critical values of the material used for producing the turbineblade. The temperature on and inside the turbine blade is reduced by thecooling gas, so that the mechanical stability and thus the operabilityof the turbine blade under these conditions are ensured.

BACKGROUND OF THE INVENTION

In this type of cooling, an outer wall of the turbine blade around whichan action fluid flows encloses a meander-shaped passage system whichrepeatedly directs the cooling gas from a root region up to a tip regionof the turbine blade and back again to the root region. The region inwhich the cooling gas is introduced is designated as leading edgeregion, and the region in which cooling gas is discharged is designatedas trailing edge region. A plurality of outlet openings are provided inthe trailing edge region, these outlet openings connecting the passagesystem of the turbine blade to an exterior space through which theaction fluid flows. During operation of the turbine, cooling gas fromthe passage system of the turbine blade discharges from the openingsright onto the surface of the outer wall.

In order to save cooling gas and thereby increase the output of the gasturbine, only as much cooling gas as is absolutely necessary in order toavoid overheating is to be used for the blades. Since many assumptionswith regard to various heat transfers are made when designing a blade,these assumptions being construed on the conservative side in order toavoid damage to the blades, and since the actual geometricalconfiguration of the turbine blades also cannot be established untilafter the casting is complete, the flow of the cooling gas through theblades is set subsequently, after the casting.

This is normally done by providing leading edge holes or aperture platesin the region of the leading edge for the cooling air entering theturbine blade, these leading edge holes or aperture plates throttlingthe entry of the cooling gas into the blade. A disadvantage in thiscase, however, is that these throttling devices have a considerable lossfactor and may in addition lead to flow separation in the region of theentry of the cooling gas, so that adequate cooling in this region of theturbine blade cannot be ensured. In addition, this configuration alsoimpairs the leading edge region, in which the pressure differencebetween first cooling chamber and external hot gas decreases.

SUMMARY OF THE INVENTION

An object of an embodiment of the present invention is therefore todesign a turbine blade which has a throttle device for setting thethroughflow of the cooling gas without influencing the flow of thecooling gas at the leading edge. Another alternative object of anembodiment of the invention is to specify a method of producing such aturbine blade. This method may be simple in terms of design and alsobeing individually adaptable.

An object may also be achieved by the throttle device being arrangedupstream of the outlet openings in the rear region of the flow path. Bysuch an arrangement of the throttle device, the throughflow of thecooling gas can be throttled without adverse effects on the flow of thecooling gas. The flow at the leading edge is effected largelyundisturbed. The throttling only begins in a rear region of the flowpath. The cooling-gas flow has left most of its path behind it and hasalready fulfilled the tasks of heat dissipation, which are linked withsufficient flow velocity.

The pressure difference between the first cooling chamber and thesurrounding hot action fluid is retained, so that no hot gas can enterthe blade, a factor which would lead to considerable damage. Reliablecooling of the turbine blade is therefore ensured. At the same time, theconsumption of cooling gas is minimized. Only as much cooling gas as isabsolutely necessary in order to prevent overheating has to be used. Inthis way, optimum cooling of the turbine blade and at the same time goodefficiency of the turbine are obtained.

Favorable flow control of the cooling-gas flow is possible if thethrottle device is attached at a reversing point of a passage. Here, thecross section of the passage and thus the throughflow of the cooling gascan be set to a predetermined degree in a simple manner. Possibledimensional differences which result from the production of the gasturbine can be rendered harmless by the throttle device. Thus the sametype of throttle device may also be used on different models of turbineblade. This reduces the number of different components of the turbineblade which are required.

It is especially advantageous if the throttle device is attached at thelast reversing point arranged upstream of the outlet openings. At thispoint, the flow path opens out, so that after that sufficient throttlingwith high efficiency is no longer possible. At the same time, thecooling gas has a maximum flow path and thus maximum contact with theinner surface of the passage system, a factor which optimizes thecooling effect.

It is especially advantageous if the throttle device is attached in alead-through opening brought about by the casting process. Lead-throughopenings, which are produced, for example, by core mounts of the castingcore during the casting, can be appropriately utilized in this way. Theyare normally closed merely by means of plates. The throttle deviceperforms the same closing function and at the same time throttles thecooling-gas flow. By means of this throttle device, it is possible toset the throughflow subsequently and compensate for any possibledimensional inaccuracies after the casting. By utilizing thelead-through openings, production steps can thus be saved, which greatlyreduces the production costs.

In order to prevent loss of the throttle device during operation or anundesirable penetration of the throttle device into the passage system,it is advantageous if the lead-through opening is permanently closed bythe throttle device. If the throttle device were to be shaken loose andwere to get into the passage system, for example during pronouncedthermal and mechanical loading of the turbine blade, considerable damageto the turbine blade or complete failure of the cooling could be caused,which would result in breakdown of the turbine within a short time. Athrottle device located outside the turbine blade inside the turbine mayalso cause considerable damage. In addition, the cooling effect would bereduced by the cooling gas being discharged into the environment at anunsuitable point through the lead-through opening, which has beencleared on account of the loss of the throttle device.

It is advantageous if the throttle device is arranged in the rootregion. As a result, the throttle device can be reached without anyproblems during inspections of the turbine blade and it is possible tocheck it for its sealing and throttling effect.

Good stability and operability are provided for if the throttle deviceis formed by a throttling projection of a plug. In this case, the plugis in each case designed in such a way that it is individually adaptedto the outside dimensions of the opening into which it is inserted. Thisis especially advantageous when the opening is a lead-through openingbrought about by the casting process, since its dimensions fluctuatewith different models of turbine blade. The throttling is effected bythe throttling projection, which fulfills its function even in a verysimple construction. The throttling projection can thus be of robustdesign while ensuring its function, as a result of which the throttledevice requires little maintenance and works reliably. The throttling isalso reliably ensured at high throughflow rates of the cooling gas andat high associated pressures or greatly fluctuating loads.

Accurate matching of the cooling-gas flow is possible if the throttledevice is formed by a foot of a screw calked in a plug. In this case,the screw is inserted into the plug, which is fastened in thelead-through opening. In this way, it is not necessary to make a screwthread in the cast turbine blade. The screw inserted into the plug canbe set in an infinitely variable manner and permits individualadaptation of the throttling to the flow requirements of the trailingedge region. The screw is locked in the desired position by thecaulking.

Fixed retention is ensured by the plug being welded in place. In thisway, the plug, with simple measures, can be accurately fastened and heldin the desired position in the opening of the turbine blade, in which itis inserted, without deforming surrounding material for example. Theopening may be a lead-through opening brought about by the castingprocess, but also an opening made in the turbine blade after thecasting, for example by drilling. In this case, the location of thethrottle device can be better adapted to the model- or casting-dependentrequirements.

An object relating to the production of a turbine blade may be achievedin that, after the casting operation, a throttle device influencing thethroughflow of the cooling gas is introduced in the rear region of theflow path in such a way as to be arranged upstream of the outletopenings. While the throughflow of the cooling gas is measured, is setup in a lead-through opening brought about by the casting process insuch a way that a predetermined value of a throughflow parameter of thecooling gas is achieved, and then the throttle device is fastenedpermanently in the throttling position.

Due to this procedure, certain cooling-gas throttling still does nothave to be taken into account during the casting operation itself. Thisfacilitates the casting operation, simplifies the casting molds andreduces the scrap. An opening brought about by the casting, for exampleproduced by a connection between the casting core and the outer castingshell, this connection holding the core in its position, can be utilizedin this way. At the same time, the throttle device closes thelead-through opening. In this way, a work step which is otherwisenecessary is saved.

By the subsequent measuring of the throughflow of the cooling gas, thecooling-gas flow can be matched individually and with simple measures tothe cooling-gas demand of a turbine blade. The setting is facilitated inthis case, since the throttling effect can be influenced from outside ina simple manner. The subsequent fastening of the throttle device in thelead-through opening may likewise be effected from outside. In thiscase, the fastening, due to the measuring of the cooling-gas flow, canbe directly controlled and if need be repeated without damaging theturbine blade.

The production method is very similar for different types of blade ifthe casting core, during the casting operation, is held in its positionrelative to the outer casting shell by a guide mount in the root regionof the turbine blade, and in that a throttle device is inserted into thelead-through opening brought about by the mount. This facilitates theproduction process and reduces the conversion time and the number ofparts to be used during the production of different types of turbineblade.

An especially simple and easily reproducible production method with lowmaterial costs is provided for by the cooling-gas flow being measured ineach case after the insertion of plugs having different throttlingprojections, and by the plug which produces a predetermined throughflowof the cooling gas being welded in place. The throttling projection isalso predetermined by the selection of a plug. Thus the plug, by a modelmeasurement, can be more or less the same for turbine blades of the sameseries. This reduces the production costs, since work steps aresimplified or dispensed with.

Individual setting of the cooling-air flow is possible by a plug havinga throttle screw, which has a throttling projection projecting into theflow path, being inserted into the lead-through opening brought about bythe casting process, and by the throughflow being measured while thescrew is adjusted, the screw then being calked in the desired throttlingposition.

The screwing position can be varied in an infinite manner during thecontinuous measurement. This permits a very accurate setting adapted tothe cooling requirements. The caulking of the screw provides forreliable fastening without damaging the material of the turbine blade.For a series of turbine blades which have approximately the same coolingrequirements and the same internal construction of the cooling passages,a screw setting determined beforehand during an exemplary cooling-airmeasurement can be marked and set. The plug with the set screw is theninserted directly into the turbine blade and the screw is calked.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in more detail with reference to theexemplary embodiments shown in the drawings, in which:

FIG. 1 shows a longitudinal section through a root region of a turbineblade with throttle device,

FIG. 2 shows a longitudinal section through a root region with a plug,

FIG. 3 shows a perspective plan view of a root region of a turbine bladewith plug,

FIG. 4 shows a longitudinal section through a root region with a plugand a throttle screw,

FIG. 5 shows a longitudinal section through a root region of a turbineblade, and

FIG. 6 shows a casting mold with a casting core.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a longitudinal section through a root region 2 and part ofa passage systems of a gas-cooled turbine blade 1. The passage system 5is located essentially in the blade-body region 3 of the turbine blade1. It has an inlet opening 22 at the root region 2, at the start of theflow path 6 of the cooling gas, through which inlet opening 22 coolinggas is passed into the passage system 5, and also outlet openings 8 inthe outflow region 21 of the turbine blade 1, through which outletopenings 8 the cooling gas leaves the passage system 5 at the end of theflow path 6 of the cooling gas.

On its flow path 6, the cooling gas is directed in a meander shape inthe passages 12, which are separated from one another by intermediatewalls 21, repeatedly from the root region 2 to the tip region (notshown) and back again to the root region 2. The passages 12 areconnected to one another by reversing points 13 which adjoin the rootregion 2 or the tip region. A throttle device 11 influencing thethroughflow of the cooling gas is located in the rear region of the flowpath 6 upstream of the outlet openings 8. The flow in the region of theinlet opening 22 is therefore not disturbed and at the same time thedemand for cooling gas is reduced.

FIG. 2 shows a longitudinal section through the root region 2 of aturbine blade with a throttling plug 20. The plug 20 is held by means ofa step 26 in a lead-through opening 10. The plug 20 has a throttlingprojection 17, with which the cooling-gas flow can be reduced in theinserted state. The plug 20 is attached at the last reversing point 13before discharge of the cooling gas from the passage system 5 in anopening in the wall 32 of the root region 2 of the turbine blade 1. Theattachment is advantageously in an opening brought about by the castingprocess, since a production step of the turbine blade 1 is thereby savedand the plug 20 at the same time sits at a point favorable for thethrottling, namely the reversing point 13 of a passage. Core-retainingpieces 29 are preferably located at these points during the casting, asshown in FIG. 6, these core-retaining pieces 29 fastening and securingthe casting core 28 relative to the surrounding casting shell 31, sothat predetermined dimensions are maintained.

By use of a curved guide rib 18, the flow path 6 is split at thereversing point 13 into two partial-flow paths: a first cooling-gaspartial-flow path 23, which is directly adjacent to the root region 2,and a second cooling-gas partial-flow path 24, which is separated by thecooling rib 18. The cooling-gas partial flows directed therethrough,after passing the guide rib 18, are united again and leave the turbineblade 1 through the outlet openings 8. The throttle device 11 throttlesthe first cooling-gas partial flow. The second cooling-gas partial flow,irrespective of the intensity of the throttling by the plug 20, flowsthrough a side passage 25 of constant size. A minimum cooling-gas flowis therefore always ensured.

FIG. 3 shows a perspective plan view of a root region 2 of a turbineblade which has a lead-through opening 10 brought about by the castingprocess and a plug 20 closing the latter. As shown in FIG. 6, thislead-through opening 10 is produced during the casting of the turbineblade 1. It has the negative shape of a guide mount 29, by which thecasting core 28, which forms the passage system 5, is connected to theouter casting shell 31, so that the casting core 28 maintains thedesired position during the casting and the subsequent cooling of thecasting material. In this case, the lead-through opening 10 is designedto be longitudinally elongated with four side walls 19.

FIG. 4 shows a detail view of a reversing point 13 with a throttledevice which is composed of a plug 20 and a throttle screw 14. The plug20 is fastened, preferably welded, in the lead-through opening 10. Thethrottle screw 14 is screwed into the plug 20. With its foot 16, whichserves as throttling projection, it projects from the plug 20 into thethrottle region 15 and thus into the first cooling-gas partial flow 23.The position of the throttle screw 14 or of its foot 16 is continuouslyvariable. In a throughflow measuring state (not shown), the throughflowof the cooling gas is measured and the position of the throttle screw 14varied until a desired throughflow is reached. The throttle screw 14 isthen fastened in the plug 20. To this end, the screw is calked,brazed-on or welded.

FIG. 5 shows a longitudinal section through the root region 2 at a 90°angle to the longitudinal section from FIG. 4. The throttle screw 14 isin the throttling position, screwed into the plug 20, which is fastenedin the lead-through opening 10. The throttling projection 17 closes thethrottle region 15, through which the first cooling-gas partial flowflows. Depending on the size of the foot 16 of the screw, only part ofthe flow path is closed, as shown in FIG. 5. However, accurateadaptation of the foot to the throttle region is also possible, as aresult of which the entire flow path in the region can be blocked.

FIG. 6 shows a casting mold 27 with casting core 28 and outer castingshell 31. The casting core 28 is connected to the outer casting shell 31via guide mounts 29, called core marks. The casting material is directedvia casting passages 30 into the interior of the casting mold 27 andsolidified. The guide mount 29 ensures that the casting core 28maintains the correct position during the casting operation and duringthe cooling of the casting material and that the dimensioningrequirements are fulfilled. After the casting operation, the guide mount29 is removed and a lead-through opening 10 brought about by the castingprocess is thus produced in its place in the root region 2 of theturbine blade 1.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

What is claimed is:
 1. A method of producing a turbine blade, includinga tip region, a root region, a blade-body region, and an inner passagesystem of individual passages, through which cooling gas can be directedon a flow path inside the turbine blade, and including a throttle deviceinfluencing the throughflow of the cooling gas, wherein cooling gas canbe directed in the passages from the root region through the blade-bodyregion to the tip region and can be diverted in the opposite direction,and also including outlet openings for discharging the cooling gas fromthe turbine blade, wherein the outlet openings are arranged on theoutflow side of the turbine blade, the method comprising: performing acasting operation with a casting mold, including a casting core and anouter casting shell; introducing, after the casting operation, athrottle device influencing the throughflow of the cooling gas, whereinthe device is introduced in the rear region of the flow path in such away as to be arranged upstream of the outlet openings and, while thethroughflow of the cooling gas is measured, is set up in a lead-throughopening brought about by the casting process in such a way that apredetermined value of a throughflow parameter of the cooling gas isachieved; and fastening the throttle device permanently in thethrottling position.
 2. The method as claimed in claim 1, wherein thecasting core, during the casting operation, is held in its positionrelative to the outer casting shell via a guide mount in the root regionof the turbine blade, and wherein a throttle device is inserted into thelead-through opening brought about by the mount.
 3. The method asclaimed in claim 1, wherein the cooling-gas flow is measured after theinsertion of plugs including different throttling projections, andwherein the plug which produces a predetermined throughflow of thecooling gas is welded in place.
 4. The method as claimed in claim 1,wherein a plug, including a throttle screw which has a throttlingprojection projecting into the flow path, is inserted into thelead-through opening brought about by the casting process, and whereinthe throughflow is measured while the screw is adjusted, the screw thenbeing caulked in the desired throttling position.
 5. The method asclaimed in claim 2, wherein the cooling-gas flow is measured after theinsertion of plugs including different throttling projections, andwherein the plug which produces a predetermined throughflow of thecooling gas is welded in place.
 6. The method as claimed in claim 2,wherein a plug, including a throttle screw which has a throttlingprojection projecting into the flow path, is inserted into thelead-through opening brought about by the casting process, and whereinthe throughflow is measured while the screw is adjusted, the screw thenbeing caulked in the desired throttling position.
 7. The method asclaimed in claim 3, wherein a plug, including a throttle screw which hasa throttling projection projecting into the flow path, is inserted intothe lead-through opening brought about by the casting process, andwherein the throughflow is measured while the screw is adjusted, thescrew then being caulked in the desired throttling position.
 8. Themethod of claim 1, wherein the method is for producing a gas turbineblade.